Liquid-liquid extraction process



Patented Sept. 8, 1953 UNI TED PATENT OFFICE LIQUID-LIQUID EXTRACTIONPROCESS .Henry Arnold-Goldsmith, Long Island city, N. :Y., assignor tofiolgaz e-Palmolivc-reet Company, Jersey City, 1,, a corporation ofDelaware No Drawing. Application March 4, 1950, Serial No. 147,761

6 Claims.

- 1 Thi invention relates to liquideliquid extraction methods forseparatin components of a mixture to prepare concentrates of the same,and more particularly to a liquid-liquid extraction process for treatinga mixtureiof lower and higher acylated esters of ,polyhydric alcoholsand fatty acids to obtain an extract phase in which the lower acylatedesters areconcentrated and .a raffinate phase in which the higheracylated esters are concentrated, and from which "the respectiveconcentrates may be separately recovered.

The discovery of the superior surface-active and emulsifying proper-tiespossessed by the less hi h y .acylated partial esters of fatty acids andpolyhydric alcohols, such as the sglycer l mono esters as compared withthe more highlyacylated glyceryi di and .tri-esters, has brought about.a demand for the production of thesepartialresters, especially the lesshighly ,acylated esters, in concentrated form. Various methods have beenused for obtaining such partial esters in concentrated or purified formcomprising molecular distillation, fractional crystallization, and thelike, which processes are either time-consuming, and produce pooryields, or, as in the case of molecular distillation, require the use'ofspecial high vacuum equipment. The resultant cost of preparing theproduct is accordingly, high.

It has now been found that the above disadvantage and drawbacks of'priormethods can be obviated for all practical purposes by employing aliquid-liquid solvent extraction process in accordance with thisinvention, and which process is admirably suited 'for commercialapplication as either a continuous or batch method.

In accordance withthe invention, compositions containing principallyamixture of less completelyacylated esters, .e. .g. monoslycerides,hereinafter referred to as iless completely lacylated esters, andmorecompletely acylatedesters, e. g. diand tri-glycerides, hereinafterreferred to as more-completely acylated esters of fattylacids andpolyhydric alcohols are subjected .toa;liquid' liquid extractiontreatment using a .tWOWDhB/SE solvent system comprising a so vent phasesuch as an aqueous lower aliphatic alcohol in which the less completelyacylated esters arepreferentially soluble and a solvent phase such .as ahydrocarbon which is immiscible with the firstmentioned liquid phaseandin which the more completely acylated esters are preferentially.so'luble. After commingling of the liquids to effect the extraction thetwo liquid phases are separated as distinct'liquid fractions which aredrawn off and which can be trea'tedto recover the solute Although theinvention will be described with particular reference to the preparationof concentrates of "fatty acid monoesters of polyhydri-c alcohols, andespecially esters of saturated and unsaturated iattyacids containingfrom about 8 to about 20 carbon :atoms per molecule, it will beunderstood that the process of the invention is'applicable generally tothe preparation of separable ziiquid :fractions in which :cer-tainacyla-tcd esters are respectively concentrated, and from which the saidesters may be recovered by removal ofthe solvent. The term esters ofpolyhydric alcohols further will lbe understood to include esters of'pol-yhydricethers of polyhydric alcohols such :as polyethylene-gly-col, polyglycerols, etc.

In the treatment 20f -fattylacid pol-yhydric alco hol esters containingless completely acylated esters and more completely acylated esterswhich are to be ;concentrat.ed, an aqueous alcoholhydrocarbon solventsystem is preferably emplayed, :it having-been round that the alcoholsolubility :of the ,fatty esters of polyhydric .alcohols decreases withincreased fatty acid substitution the -molecule. Employing such anaqueous alcohol-hydrocarbon solvent system, the less completely acylatedesters which are preferentially soluble in the aqueousaalcoholic phasecan be concentrated in this phase and separated as animmiscible vliquidfrom the remainin 11yclrocarbon solvent phase in which themorecornpletely acylated esters are preferentially soluble. The reactionproducts obtained by esterifyihg lycerol, for exam le, with iatty acids,or by the lvcerolysis of iglycerides, .are usually mixtures of mono e,(11-, and minor amounts of .tri-glycerides even when the excess ofglycerol .used is considerable. Such mixtures are known and sold n thevarious trades as "imonog1ycerides even though their actualmonoglyceride content generally ranges .onlyirom about 30 to Therecognized superiority, however, of monoglycerides over ,diglycerides,as surface-active agents, as Well as their known value in thepreparation Ql lnonwsoap detergents, has increased th desirability ofobtaining monoglycerides of the fatty acids in concentrated form. 7

The liquid-liquid extraction process of the present invention provides amethod for effecting this, the extraction preferably being carried-outin repeated stages with fresh solvent, in a continuous countercurrentextraction flow, or as a batch counter-current method, as desired.

The alcohols employed in the solvent system for-effecting theliquid-liquid extraction of Iatty acid monoglycer'ides from mixturescontaining v mono-, diand tri-glycer'ides, are preferably thewater-soluble lower aliphatic alcohols :(e. g. conincorporating suitableamounts of water in the alcohols the resultant liquid mixture is causedto separate into two phases, one containing prin-- cipally aqueousalcohol in whichthe mono ester 1 is dissolved and another containingessentially the hydrocarbon solvent in which are dissolved a major partof the diand triglycerides. Al-

though the two liquid phases do not consist of pure solvents, theaqueous alcohol phase functions as a preferential solvent for the monoesters whereas the hydrocarbon solvent forming the raflinate phasefunctions as a preferential solvent for the diand triglycerides.

The proportion of water required in any particular case depends upon thesolvents'used, the material being treated, as well as the yield andpurity desired. In concentrating glycerol monostearates from mixturescontainin principally monoand di-stearates of glycerol, the purestmonoglycerides were obtained using approximately 100 volumes of ethylalcohol to 20 volumes of water. In the case of lower fatty acid esterssuch as glyceryl monolaurates, approximately 55% ethyl alcohol and 45%water by volume has been found to be the most efficient for effectingthe preferential liquid separation of the monolaurates. With theapplication of the process to the recovery of other monoglycerides andmono ester of glycols and fatty acids the water content of the alcoholwill vary and can be readily determined by trial methods so as toprovide for proper liquid phase separation. In multiplestageextractions, preferably somewhat more than the minimum amount of wateris used which will cause the liquid phase'separation to be accomplishedat the temperature of treatment, particularly where a high extract yieldis desired. The process is readily effected at room temperature, that isbetween about 20 and 30 C. Higher or lower temperatures may of course beused, and in some cases may be desirable, but in general the processwill be carried out at ordinary room temperatures.

In successive five-stage extraction treatments employing a systemconsisting of n-octane-ethanol and water, it was observed that in thetreatment of a mixture of lauric acid glycerides, comprising 80% byweight monoglyceride, it required a solvent system containing about 27%or more (by volume) of water to yield extracts of a purity of over 90%by weight mono ester. Somewhat less water may be used, however, in thecase where methyl alcohol is employed in place of ethyl alcohol. In asimilar system, the extraction of a mixture of myristic acid glyceridescontaining 57.9% by weight mono myristin, produced extracts of anoptimum purity of 86% monomyristin when the system contained 20% (vol.)of water. Beyond this dilution, the purity of the extract in mono esterdecreased. With a mixture of palmitic acid glycerides containing 55.6%by weight monopalmitin, the extract reached an optimum purity of 88%monopalmitin wherethe system contained approximately 11% (vol.) ofwater. In the case of a mixture of stearic acid glycerides containing52.5% monostearin, the extracts of the monoglyceride were 90% pure wherethe system contained above about 9% (vol.) of water.

Where the ester mixture being treated contains appreciable amounts offree glycerol the mixture is best pretreated to remove the freeglycerol. If this i not done, the amount of water must b correspondinglyreduced in order to compensate for the presence of glycerol. Thefollowing examples illustrate how the process may be utilized,the'percentage parts given having reference to weight unless otherwisestated. The monoglyceride content in the examples given was determinedby the periodic acid oxidation method.

' Example 1 Twenty-two and a half grams of a commercial stearic acidmixed glyceride, composed of 57.3% monoglyceride and 42.7% diglyceride(together with minor amounts of triglyceride) is dissolved in 100 ml. ofn-heptane, the commercial stearic acid being composed of a mixture of43% stearic, 51% palmitic, and 6% oleic acids. To the resultant solutionis introduced 100 ml. ethyl alcohol and 20 ml. water, and the solutionsshaken. Upon separation of the phases, and evaporation of solvent fromthe separated phases, the extract in the aqueous alcohol phase was foundto contain 26.2% of the monoglyceride present in the form of a mixtureof 83.3% monoglyceride and 16.7% diglyceride of the commercial stearicacid. Although, as will be observed, the yield is low employing a singlestage treatment the purity of the extract in monoglyceride is relativelyhigh.

Example 2 To 18 grams of a mixed glyceride, composed of 59.2%monoglyceride and 40.8% diglyceride (with minor amounts of triglyceride)of the commercial stearic. acid of Example 1, dissolved in ml. octane, amixture of 100 ml. 95% ethyl alcohol and 12 ml. water was added, thesolutions shaken, allowed to separate into phases, and the solvent fromeach of the phases evaporated. The aqueous alcohol extract was found tocontain 52.2% of the monoglyceride present in the form of a mixture of81.1% monoglyceride and 18.9% diglyceride of the commercial stearicacid. In this example by the use of a lesser proportion of water than inExample 1 the yield of mono ester was increased but the purity of theextract in monoglyceride was lowered.

Example 3 A 22.5 gram sample of the mixed glyceride described in Example1 was dissolved in 100 ml. of commercial n-heptane and extracted byshaking outwith a mixture of 100 ml. 95% ethyl alcohol and 20 ml. water.The aqueous alcohol phase was separated and extracted with 4 successive100 ml. portions of fresh n-heptane; the n-heptane phase was extractedwith 4 successive ml. portions of aqueous alcohol, and each alcoholicextract was shaken out successively with the successive portions ofn-heptane mentioned above. Thus, every one of the aqueous alcoholportions are extracted by each of the n-heptane portions, and viceversa. The combined aqueous alcohol extracts contained 80.3% of themonoglyceride present in the form of a mixture of 91.2% monoglycerideand 8.3% diglyceride of the commercial stearic acid.

A 54.6 gramsampleota mixedglyceride, composed .of 47.6% :monoglycerideand 52.4% of diglyceride .(containing minor proportions ofltriglycerides) of coconut oil .iatty .acids =was .ex tracted withlive200 .mLmort-ions :of commercial n-hep-tane ,and five .portions eachof .200 .ml. methanol .and 40 .ml. water, proceeding as .described inExample 3. The combined aqueous methanol extracts iconta-ined 185.4%-.of the monoglyceride present .in the form of .a mixture-of 75.6%'monoglyceride .and.24.4% or diglycerideof coconut oil .fatty .acids.

' Example 5 .A 22.6..gram a p-1e are mixed .glyceride. composed .of56.2%,monoglycer'ideand 433% dig'lyc- .eride of .a commercial .oleic.acid Ki. .e. .a mixture of .85 -:O1BiC., 3% .linoleic. and .7 palmiticacids.) was .extracted with five .100 ml. portions or commercial.n.-heptane and .fiveportions. each of 100 ml- 95% ethyl alcohol and.30. ml. water proceeding as described in Example 3. The combinedaqueous alcoholiextractscontained 78.4% .of the monoglyceride present in.theiorm of .a mixture oI:93.-4% monoglyceride and-6.6.% diglycer-ide ofthe connnercial oleic acid.

Example fi dissolved in 200 ml. of commercial n-heptane was placedinside a simple =4-foot glass column of 24 mm. .inner diameter which.was packed in its centralsection (33 inches high) with flfliserlsaddles. Amixture of '600 m1.95.% ethyhalcohol and 150 ml. water waspumped through "Zthe column, from the top, at the'rate of 600nil.perhour, and the aqueous alcohol phase emerging at the bottom was drainedand evaporated. The extract thus obtained contained 85.17% of themonoglyceride present in the form of a mixture of 92.5% monoglycerideand 7.5% diglyceride of the commercial stearic acid.

Example 8 A twelve-stage, agitated, counter-current column essentiallyas described by E. G. Scheibel (Chemical Engineering Progress 44,681-90; 771-82, 1948) was employed as a convenient counter-currentdevice in the extraction treatment of a commercial mixed glyceridecomposed of 59.2% monoglyceride and 40.8% diglyceride of commercialstearic acid, as described in Example 2. During the counter-currenttreatment, a 26.1% by weight solution of this glyceride mixture in theextraction system (47.16 volume percent of commercial n-octane, 47.16volume percent of 95% ethyl alcohol, and 5.68 volume percent of water)was fed into the column at the eighth mixing zone upward, thus dividingthe column into seven stages below and four stages above the feed stage.The glycerideisohition' forms a. clear liquid which permits theglyceride to be -easily introduced into thecolumn and which solutionwill readily separate "into two "liquid phases -=upon dilutionwith moresolvent. "To bring this liqu-i'd phase -separation about and provide thedesired selective solvent phases, octane was fed into the columnat thebottom, and a 100912 by volume mixture of 95% ethyl alcohol and water,respectively, fed at the top by means of small pumps. A'stirringrotational speed'of 1200 R. '1. M. ;;provided -=eificient agitation ofthe col-umn contents. The best extraction results were obtained bysetting the pumping ratesof the three feed pumps in such aratioas toproducean'equilibrium concentration'of Elite 46 grams of glyceridesperliter' of solutions at the-topand bottom 'ofthe-cdlumn. Carryingouttheextractionas described employ ing an equil'flrrium concentrationof '46 grams glyc eride per liter, 89.5% of the :mon'oglycerideifed intothe "mixture "was extracted by the aqueous alcohol phase and in :theformof amixture of 92%monog'lycerideand 8 of diglyceride ofthe commercial"s'tearic acid.

The "results, as measured by extraction yield and extract fipurity, maybe varied "by changing. the concentration of the -mixed 'glyceride feed,the pumping'rates,'the rotational speedo'f the'column agitation, and thesolvent composition. Also the mixed .g'lyceride may befedtnto themixturein the .form of a melt where suitable designed extraction equipment isutilized.

Example 9 ethyl alcohol and "8 ml. water. The alcoholic extractcontained 360% .of the diethylene glycol monoester presentin the [formof a mixture of monoester and 20% diesterlcalculated from .thesaponification value of the extract) Example :10

.A;210.gram,sarnple of an .ester mixture obtained .=by.readting one.mole of a polymerized glycerol -.(.conihiriing weight 186;approximately 75% of .dig1ycerol,.25,% of f triglycerol and small:amounts oIt-lii gherpolyglycerols') with two moles ofcommercial stearicacid was dissolved'in 200 m1. 'c'om-' mercial n-octane, and the solutionextracted with a mixture of 200 ml. 95% ethyl alcohol and 8 ml. water.The alcoholic extract contained 49.5% of the sample as a soft, toughsolid which swelled up in hot water and could be dispersed by addingsome alcohol; the raflinate in the octane phase was a brittle, andcomparatively hard solid which did not disperse in water at all. Thesaponification values of the starting material, the extract, and therafiinate were 166, 153 and 181 respectively, indicating that theextract was poorer and the raflinate richer in fatty acid than thematerial subjected to extraction.

Example 11 A 40 gram sample of an ethylene glycol ester of a commercialoleic acid composed of 73.5% monoester and 26.5% diester (refractiveindex at 25 0., 1.56202) was dissolved in 200 m1. of commercialn-octane, and the solution extracted with a mixture of 200 ml. methanoland 8 ml. water. The methanolic extract contained 45.2% of the sample inthe form of a mixture of 78.5% monoester and 21.5% diester (refractiveindex at, 25 (3., 1.46170).

, The process of the invention provides many advantages over priormethods of obtaining these partial esters in concentrated form,particularly as regards simplicity of operation and commercialadaptability. As heretofore pointed out, the process is not only capableof wide variation with respect to the ester mixtures which may berefined, but also the operating procedure and arrangement may be variedto suit the particular conditions and uses to which the invention may beput. 7

As many widely difierent embodiments of the invention may be madewithout departing from the spirit and scope thereof, it is to beunderstood that the same is not limited to the specific examples orembodiments hereinbefore setforth except as defined in the followingclaims.

What is claimed is:

1. A process of treating an ester product containing principally amixture of less completely and more completely acylated esters of fattyacids and polyhydric alcohols which comprises contacting said esterproduct with water, a water miscible lower aliphatic alcohol, and a lowboiling aliphatic hydrocarbon, said alcohol and hydrocarbon beingmiscible and said water being present in an amount sufficient to causethe formation of two immiscible liquid phases, one phase comprisingaqueous alcohol in which a major proportion of said less completelyacylated esters are dissolved and one phase comprising the hydrocarbonin which a major proportion of said more completely acylated esters aredissolved, and

separating said two liquid phases.

r 2. A process as set forth in claim 1 in which said ester product issubjected to liquid-liquid extractionwith said water, alcohol andhydrocarbon by continuous countercurrent flow.

I 3. A process of treating a glyceride product containing a mixture ofmonoand diesters of fatty acids and glycerine to produce a liquidextract in which the glyceryl mono fatty acid ester is concentrated anda liquid raflinate in which said glyceryl di fatty acid ester isconcentrated which comprises intermingling the glyceride product withwater, a lower aliphatic monohydric alcohol containing about 1 to 4carbon atoms, and a low boiling aliphatic hydrocarbon, said alcohol andwater being miscible and said Water being present in an amountsufiicient to cause the for- 8 mation of an aqueous alcohol extractphase in which said monoesters preferentially are dissolved and ahydrocarbon rafiinate phase immis cible therewith in which said diesterspreferentially are dissolved, and separating said extract and raffinatephases.

4. A process as defined in claim 3 in which the glyceride producttreated consists principally of a mixture of glyceryl monostearate andglyceryl distearate.

5. A process of extracting a liquid fraction containing monoesters offatty acids and glycerol from a fatty acid glyceride mixture comprisingsaid monoesters together with fatty acid diesters which comprisescontacting said glyceride mixturewith water, a lower aliphaticmonohydric alcohol containing about 1 to 4 carbon atoms, and a lowboiling aliphatic hydrocarbon, said alcohol and hydrocarbon beingmiscible and said water being present in an amount suflicient to formtwo immiscible liquid phases, said monoesters be-'- ing dissolvedselectively in one of said immiscible liquid phases, withdrawing saidliquid phase containing said monoesters dissolved therein, and removingthe solvent to recover the monoesters substantially free of saiddiesters.

6. A process of treating a mixture comprising mono-, diand triglyceridesresulting from reacting fatty material with glycerine to separate themonoglycerides therefrom which comprises subjecting the glyceridemixture to liquid-liquid extraction with water and a mixture of misciblesolvents comprising ethyl alcohol and n-heptane, said water beingpresent in an amount suflicient to produce a liquid extract phasecomprising principally said monoglycerides dissolvedin said ethylalcohol and water and a liquid raflinate phase immiscible with saidextract phase comprising principally said diand triglycerides dissolvedin said n-heptane, withdrawing said 'extract phase, andremoving thealcohol and water therefrom to recover said monoglycerides substantiallyfree from said (111- and triglycerides.

' HENRY ARNOLD GOLDSMITH.

References Cited in the. file of this patent UNITED STATES PATENTSNumber Name Date 2,200,391 Freeman May 14, 1940 2,290,609 Goss July 21,1942 2,553,288 Young et al May 15, 1951

1. A PROCESS OF TREATING AN ESTER PRODUCT CONTAINING PRINCIPALLY AMIXTURE OF LESS COMPLETELY AND MORE COMPLETELY ACYLATED ESTERS OF FATTYACIDS AND POLYHYDRIC ALCOHOLS WHICH COMPRISES CONTACTING SAID ESTERPRODUCT WITH WATER, A WATER MISCIBLE LOWER ALIPHATIC ALCOHOL, AND A LOWBOILING ALIPHATIC HYDROCARBON, SAID ALCOHOL AND HYDROCARBON BEINGMISCIBLE AND SAID WATER BEING PRESENT IN AN AMOUNT SUFFICIENT TO CAUSETHE FORMATION OF TWO IMMISCIBLE LIQUID PHASES, ONE PHASE COMPRISINGAQUEOUS ALCOHOL IN WHICH A MAJOR PROPORTION OF SAID LESS COMPLETELYACYLATED ESTERS ARE DISSOLVED AND ONE PHASE COMPRISING THE HYDROCARBONIN WHICH A MAJOR PROPORTION OF SAID MORE COMPLETELY ACYLATED ESTERS AREDISSOLVED, AND SEPARATING SAID TWO LIQUID PHASES.